Amphoteric surfactants are used on a large scale for the preparation of toiletries, particularly for the preparation of shampoos. One therefore strives to synthesize the amphoteric surfactants free of impurities, which can cause skin irritations or are undesirable in some other way for physiological reasons. These include also residual amounts of compounds with organically linked chlorine, particularly sodium dichloroacetate, which is introduced directly into the end product along with the chloroacetic acid raw material or its salts. Attempts to reduce the content of sodium dichloroacetate by employing longer reaction times or higher pH values, did not lead to a significant decrease in the dichloroacetate content. The use of higher pH values, particularly those above 10.5, entails the risk of increasingly decomposing the product.
The German Offenlegungsschrift 39 39 264 relates to a method for lowering the residual content of free alkylating agent in aqueous solutions of amphoteric or zwitterionic surfactants, with the requirement that the solutions are given an aftertreatment with ammonia, amino acid with 2 to 8 carbon atoms or oligopeptide. By means of this aftertreatment, the residual content of free alkylating agent, particularly of chloroacetic acid, is to be reduced to values below 0.01% by weight (based on the solids content). A significant disadvantage of this method lies, however, therein that an additional process step is required. A further disadvantage can be seen therein that the products of the reaction of the alkylating agent with ammonia, an amino acid or an oligopeptide remain in the process product as impurity.